Vitamin D in a Scottish winter

Starting a thread on this because it keeps coming up in ones and twos: Vitamin D in a Scottish winter

I have read the paper and I am not sure I have understood it.

I have a document in front of me and I can read every line of it and I still cannot tell what it proves.

I would like to know what the best single piece of human evidence is, because I suspect the honest answer is thinner than the discussion suggests.

What I want is the methods rather than the conclusions, because I have been burned by a conclusion that the methods did not support.

Thanks. I would genuinely rather be told nobody knows than be given a confident answer.